Wild horses in the Yukon are classified by the territory as "feral animals," but some advocates and biologists want to change that, saying the animals should be considered a native species.

"'Feral' ... has a negative connotation, and just isn't an accurate word for them, since the current wild horses have never been domesticated," said Heather Brown, of the Friends of the Yukon Wild Horses Society.

Wild horses in the Yukon are found around the Ibex Valley, west of Whitehorse. The society keeps track of the animals with trail cams and has identified 21 horses in the herd, though the exact number of animals is not clear.

Those animals have been "completely wild" for about 30 years according to the society, but it's not known whether they are descended from outfitters' horses that became feral decades ago, or can be traced back to horses from the Klondike Gold Rush era.

The horses are afforded some protections under the Animal Protection and Control Act, which makes it illegal to hurt or kill them. However, they are managed differently than other ungulates, like caribou, elk and bison, which are considered wildlife and are managed under the Wildlife Act, says the Yukon's Department of Environment.

Aud Fischer, another member of the Friends of the Yukon Wild Horses Society, says that some people view wild horses as an invasive species. She disagrees because Yukon was also home to wild horses during the last ice age.

"They are viewed as feral because they've had the 4,000 or 5,000 years of domestication in between," Fischer said. "And so people, a lot of people, view them as invasive and a danger to ecosystems and as nuisance animals."

She believes wild horses should be considered a "reintroduced native species" and wants the Yukon government to develop a "humane management plan" to protect them.

The Wildlife Act protects vertebrate animals that are "wild by nature," says the Department of Environment — excluding wild horses. The Yukon Conservation Data Centre, which collects data on vulnerable or at-risk species to inform conservation plans, also does not collect the such data for wild horses, because they are considered feral.

That means that right now, wild horses in the territory do not have a conservation status and there is no management plan in place for them. However, if they were to be considered a native species that could change.

The status of Yukon's wild horses also reflects a larger debate about the origins of wild horses across North America and comes at a time when the concept of a native species is changing.

However, the debate is contentious, as there is also evidence that wild horses could have a negative ecological impact if populations reached a high enough threshold.

Ross MacPhee, a paleomammologist and curator emeritus of mammals at the American Museum of Natural History, says native species are those that originate in a particular area, or moved there naturally.

"'Nativeness' generally means animals or species that originated in a particular place and are therefore in the genes," MacPhee said. "But broadened also to include, bio-geographically, species that originated elsewhere but have moved into the area of interest, by their own means. In other words, humans weren't involved."

For a species to be considered "invasive," however, requires more than proof of non-nativeness, says Bruce Bennett, a retired biologist and member of the Yukon Invasive Species Council.

"They have to be exotic, so they have to have been introduced with the help of humans," Bennett said. "But then you have to look at the second part of it, which is they have to be causing economic or environmental harm."

Bennett says that with climate change, many species once considered non-native to the territory are expanding their ranges. He expects our understanding of what makes an invasive or native species will also continue to evolve.

DNA and fossil evidence suggests that horses native to North America went extinct on the continent sometime between 13,000 and 6,000 years ago.

Domesticated horses that were later brought to the Yukon are descendants of wild horses that originated in Central Asia.

However, MacPhee says that wild horses in the Yukon today do share some DNA and evolutionary history with native horses that once roamed this continent.

Prior to the extinction of North American native horses, the Bering Land Bridge — a strip of land that once connected Asia to Alaska — allowed some interbreeding to occur between Eurasian horses and North American horses. That interbreeding was not enough to merge the two species, but does explain why today's horses do share some DNA with extinct horses that were native to the continent.

Despite the fact that the Yukon's wild horses are not direct descendants of horses native to North America, MacPhee says they fulfil the same ecological role that native horses once did. He believes they should therefore be considered native species, even though they were introduced by humans.

Part of that ecological role is helping to preserve North America's grasslands.

"They play a substantial role in things like seed distribution, which seems, you know, kind of a minor thing, but it really isn't when you're talking about native grasses," MacPhee said. "Many of them actually rely on the vertebrates distributing their seeds. And since that doesn't happen anymore, at least on the scale that it did in the past, you have a situation in which grasslands have been retreating."

MacPhee says grasslands are a biome that stores a great deal of carbon, potentially even more than forests.

That's why he believes wild horses could play an indirect role in reducing greenhouse gas emissions by helping grasslands expand, and why there is a common interest in managing wild horses like a native species.

The Yukon government says some studies suggest that wild horses could negatively affect other ungulates, like elk, sheep, bison and caribou.

In a statement to CBC, the Department of Environment said that a study it conducted in collaboration with the University of Calgary in 2013 found that wild horses could limit the number of elk that Yukon's Tahkini Valley can support.

Another study, completed in 2015 in conjunction with the University of Alberta, found that wild horses have the potential to compete with elk, caribou, sheep and bison for food and habitat. In particular, the diet of wild horses overlaps significantly with that of bison.

Yukon's Department of Environment expects that the negative ecological effects of wild horses would increase with their population. However, due to a lack of research, the extent of wild horses' impacts on the surrounding ecosystem remain unclear.